The Relationship between rs534654 Polymorphism in TMEM165 Gene and Increased Risk of Bipolar Disorder Type 1

Bipolar disorder (BD) is a major health care concern worldwide. There are some reports showing an association between genes and their variants involved in circadian rhythm; clock and clock related genes function and development of BD in patients. Therefore, the aim of this study was to investigate the possible association of rs534654 variant on TMEM165 (transmembrane protein 165) gene with the risk of BD. Genotyping of the rs534654 was carried out using the tetra primers- amplification refractory mutation system-PCR (4P-ARMS-PCR) method in 203 patients with BD type 1 and their healthy and normal counterpart. The frequency of the G and A alleles of rs534654 polymorphism was 53% and 47%, respectively in patients. Genotype frequency in patients in comparison with control subjects was 5.4% vs 2.5% for the AA homozygous; 11.3% vs 80.8% for the GG homozygous; and 83.3% vs 16.7% for the heterozygous AG. Statistical analysis showed a significant diﬀerence in frequencies between the control and patient groups (P = 0.001). Based on this finding, it is possible to conclude that the impairment in the rs534654 single nucleotide polymorphism in TMEM165 gene is associated with the risk of BD development.

need for sleep is reduced whereas depression episodes' experience hypersomnia (6,7). Genetics background is complicated in BDs with high heredity (H_85%), and it involves many genes and potential interactions between them and environmental factors (4). It has been shown in our previous reports that changes in BDNF (brainderived neurotrophic factor), ADCY2 (adenylate cyclase 2) genes play an important role in the development of BD (8,9). The human body is ruled by several sorts of rhythms. In addition to previously described genes and their controlling pathways, in mammals, the circadian rhythms are controlled by the brain (10). The central core of endogenous circadian clock is located in the superchiasmatic nuclei of the hypothalamus (11).
Dysfunction of circadian rhythm, clock and clock related genes, all affect the pathophysiology of BD (12). Clock gene transcription and translocation, play an important role in circadian rhythm (13,14).
The TMEM165 gene is one of the genes adjacent and overlapping with a clock gene which is located on chromosome 4 but transcribed from the opposite strand (15)(16)(17), and it is possibly involved in circadian cycle. A large number of classical genetic association studies revealed the role of circadian genes in predisposition to MD (18,19). Human TMEM165 gene encodes 7 transmembrane protein domains which are calcium/proton transporter. Moreover, it has a role in regulating Ca 2+ and pH lysosomal homeostasis, and is mainly located in Golgi apparatus (16,20,21 test was also used for comparing genotype and allelic frequencies between the BD subjects and controls. The P-values were two-sided and a P < 0.05 was considered as statistically significant differences in all analyses.

Results
The subjects in the control and patient groups were compared for demographic features such as sex and age. The mean age of the patients and controls were 43.23±11.2 years and 36.63 ± 9.42 years respectively. The demographic data of the selected patients showed that more than 53.2 percent of the cases were males.

Evaluation of demographic indicators
Differences between groups were assessed by t-test with Mann-Whitney formula (MS). There was The specific band related to each genotype of the rs543654 SNP is shown in Figure 1.  A positive association between SNP rs534654 and BD in the genotypic distributions (P = 0.001), (Table 3) was observed.

Discussion
BD has a complex genetic background. In the present study, it was found that more than 51.2% of patients had related history in their family, supporting the fact that a significant relationship may exist between heredity and BD (4,29). It was reported that the largest onset age of BD is between 20-40 years old (30), which in the present study has also been the highest age of onset in patients group.
The present study assessed the association between the rs534654 in TMEM165 and the risk of According to the results of this study, rs534654 variant of TMEM165 could be considered as a potential risk factor of BD. Additional studies are also necessary to find other associated variants of TMEM165 gene and understanding the underlying mechanism by which the rs534654 SNP influences the susceptibility to BD.

Conflict of Interest
Authors declare no conflict of interest.